This invention relates to a mechanical positioning technique and, more particularly, to such a technique useful in positioning cylindrical articles, such as optical components, in a production setting.
When an optical system involving free-space propagation of light beams is constructed, the optical components must be aligned to a high degree of precision. Any misalignments lead either to a loss of beam energy or to inoperability of the optical system if the misalignment is too large. When there are multiple optical components to be aligned, the beam losses due to misalignment multiply as the beam propagates through each successive optical component.
There are highly sophisticated alignment devices suitable for laboratory or prototype work. These devices allow adjustment in five or six degrees of freedom as required for general alignment. Such devices are costly and are not suitable in many cases for the positioning of production components because portions of the alignment device remain in the production device after the alignment is complete and therefore must be treated as a consumable item.
In the production setting where the cost of consumable portions of the alignment apparatus is a concern, components to be aligned are typically supported from a baseplate on dowel pins or wires and then carefully positioned. Supports such as dowel pins and wires have the shortcomings that they do not permit movement of the optical component in five or six degrees of freedom and in some cases are highly compliant so that they do not retain the aligned position. Thus, these approaches have shortcomings in the production environment.
There is a need for a positioning approach that allows an optical component to be positioned precisely in the production setting. That is, any parts of the alignment apparatus that remain in the aligned optical system must be inexpensive and disposable. The apparatus and approach must permit a high degree of precision in the alignment. The present invention fulfills this need, and further provides related advantages.
The present invention provides an alignment apparatus and method for positioning a cylindrical article with up to six degrees of freedom. The approach produces a highly precise alignment, both temporarily and permanently. The alignment is achieved with a metal-to-metal contact that is rigid. The portions of the alignment apparatus that remain in the aligned optical system are inexpensive and disposable. The present approach is particularly suitable for the alignment of articles in a production setting. While the approach is specific to cylindrical articles, many otherwise non-cylindrical articles may be placed into a cylindrical housing for alignment by the present approach.
In accordance with the invention, a method for positioning a cylindrical article comprises the steps of providing a support surface, and providing a cylindrical article having a cylindrical axis, a cylindrical surface, a first end of the cylindrical surface, and a second end of the cylindrical surface. The cylindrical article is preferably a component of an optical system such as a collimator. If the article is not initially cylindrical, it may be mounted in a cylindrical housing to permit the practice of the present approach. The cylindrical article is supported from the support surface by a first pair of bearings contacting the support surface and the cylindrical surface adjacent to its first end, with one bearing of the first pair of bearings on either side of a projection of the cylindrical axis onto the support surface, and a second pair of bearings contacting the support surface and the cylindrical surface adjacent to its second end, with one bearing of the second pair of bearings on either side of the projection of the cylindrical axis onto the support surface. The cylindrical article is positioned by moving at least one of the bearings relative to the cylindrical article.
The bearings are preferably ball bearings that provide six degrees of freedom in the movement of the cylindrical article. Other types of bearings may be used where appropriate. For example, roller bearings may be used where motion of the cylindrical article parallel to the cylindrical axis is not required.
Any of an operable combination of three approaches is preferred for constraining the movement of the bearings in the desired paths and in the desired locations. In the first approach a first linear constraint is formed in the support surface, and a second linear constraint is formed in the support surface parallel to the first linear constraint. The first pair of bearings is placed into the first linear constraint, and the second pair of bearings is placed into the second linear constraint. The use of the linear constraints causes the movement of the pairs of bearings to be parallel to each other along the surface of the support surface, and generally perpendicular to the projection of the cylindrical axis onto the support surface. (xe2x80x9cGenerally perpendicularxe2x80x9d means that the relation is either exactly perpendicular or nearly perpendicular to within a few degrees, such as within about 5 degrees.)
In a second approach, the support surface is magnetized, and the four bearings are made of a ferromagnetic material. Equivalently but less conveniently, the four magnetized bearings may be magnetized, and the support surface is ferromagnetic. This use of magnetic force biases the bearings in place, requiring a positive force to move them.
In the third approach, a biasing force is applied to the cylindrical article in a direction perpendicular to and toward the support surface. This biasing force may be applied by any operable approach such as, for example, a mechanical actuator or an applied magnetic field.
The bearings are moved in a coordinated fashion to reposition the cylindrical article in four degrees of freedom. To raise or lower the cylindrical article in a direction perpendicular to the support surface, the bearings of both pairs are moved on the support surface and in a direction generally perpendicular to the projection of the cylindrical axis, so that a spacing between the bearings of each pair changes by the same amount. To change the pitch of the cylindrical article relative to the projection of the cylindrical axis onto the support surface, the bearings of both pairs are moved on the support surface and in a direction generally perpendicular to the projection of the cylindrical axis, so that a spacing between the bearings of each pair changes by a different amount. To move the cylindrical axis parallel to the support surface and perpendicular to the projection of the cylindrical axis onto the support surface, the bearings of both pairs are moved on the support surface and in a direction generally perpendicular to the projection of the cylindrical axis, so that a spacing between the bearings of each pair is unchanged. To change the yaw angle of the cylindrical article, the bearings of one pair are moved on the support surface generally perpendicular to the projection of the cylindrical axis, so that a spacing between the bearings of each pair is unchanged. A fifth degree of freedom is attained by rolling the cylindrical article on the bearings parallel to the cylindrical axis. A sixth degree of freedom is attained by rotating the cylindrical article about the cylindrical axis on the bearings.
The present approach is preferably practiced in an automated fashion. An actuator system moves the bearings. A feedback control system comprises a sensor having as a sensor output an indication of a position of the cylindrical article, and a controller having the sensor output as an input and a command signal to the actuator system as an output.
When the cylindrical article is temporarily positioned to its desired final position, it may be fixed relative to the support surface. The fixation may be accomplished temporarily, as with mechanical clamps or other devices, or permanently, as by potting the structure, including the bearings, with epoxy or other potting material. The bearings, relatively inexpensive articles, remain in the permanently fixed structure and are therefore consumables.
The present approach is readily practiced in a production setting, so that the alignment and permanent fixing of the cylindrical article are accomplished accurately and inexpensively. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.